By Piers Scholfield BBC News, Washington

The suburbs of the US are no longer the same as those immortalised in 1950s movies, with white families living in big houses and the father driving off to work in his Buick, past manicured lawns.

MS-13 gang members are often heavily tattooed

These days, it is more likely that English will not even be the first language you hear on the streets.

In Langley Park, Maryland, the kiosks sell Spanish-language newspapers; the supermarket shelves are stocked with tortillas and assorted black beans.

Mexican music plays in the background while the tannoy blares out announcements in Spanish.

Outside, groups of men hang out on the street corners and their Spanish is accented - Nicaraguan, Honduran and, most often, Salvadoran.

They wait, hoping to be picked up for a day's labouring in the houses and gardens of Washington DC's middle class.

But among the hard-working families lurks a darker shadow.

Violent crime

Vicious street gangs, committed to violence, have spread throughout the Americas and are now a significant threat in the US.

We visited Maria Hernandez in her apartment in Langley Park.

She welcomed us through her battered front door, which had been smashed by police in a dawn raid.

The groups spread to Central American states after being born in the US

They were looking for evidence connecting her son, Marvin, to an assault, where a man suffered brain damage after being hit on the head with a baseball bat.

Maria told us that Marvin had joined a gang after being picked on at school.

The police search warrant said Marvin was a member of MS-13.

MS-13 - or Mara Salvatrucha - is the biggest and fastest-growing of the Latin American street gangs.

In Maryland alone, MS-13 members are accused of being responsible for a long series of violent crimes including murder.

Favoured tactics include decapitation by machete.

MS-13 started life as a group of young immigrants on the streets of California in the 1980s.

After nearly a million Salvadorans fled their civil war for the US, many of them settled in Los Angeles where gang violence was rife.

In the 1990s, the "maras" spread to Central America after many of their leaders were deported from the United States.

Kill and control

Those countries, struggling to get back on their feet after years of devastating civil conflict, were a perfect setting in which gangs could proliferate.

There's evidence that the model of the gang is rape, kill, control. They're really about gaining control over other immigrants from their community Rod J Rosenstein, US attorney for Maryland

Rod J Rosenstein is Maryland's US Attorney.

His office is currently prosecuting a series of cases against MS-13. He told us the gang's motives are more about mayhem than money.

"There's evidence that the model of the gang is rape, kill, control," he said.

"They're really about gaining control over other immigrants from their community, intimidating people and asserting some degree of threat which enables them to control their neighbourhoods."

Rosenstein's prosecutors have moved on from charging individual gang members with discrete crimes.

Instead, they are now targeting MS-13 with federal racketeering laws - the same legislation used against the Mafia and other organised crime.

For this tactic to be successful, they must prove that MS-13 is indeed an organised network.

We attended court in Greenbelt, Maryland.

The prosecutors spent much of their time talking about gang meetings; about the clothes - blue and white for MS-13 - and the tattoos.

And, most damningly, an alleged firm link between gang leaders in El Salvador and their proteges in the US.

Murder by mobile

In June 2007, the then US Attorney-General, Alberto Gonzales held a press conference to announce charges against MS-13 leaders in El Salvador.

Police seem unable to crack the strength of the gangs

The indictment alleged that Saul Antonios Turcos Angel communicated with members of the "Teclas Locos Salvatruchos" clique in Maryland via mobile phone and ordered them to commit two murders.

Later that day gang members in Maryland killed two people and wounded a juvenile.

The links between the countries are clear.

The court in Greenbelt was shown a home video made by the gang in a Salvadoran prison.

In it, maras send greetings to their "homies" in Maryland and other parts of the US.

They talk of killing and controlling others and display their full-body tattoos in a show of allegiance to MS-13.

Mindful of these trans-national links, the FBI last year made the decision to open an office in El Salvador.

Aaron Escorza heads the FBI's National Gang Task Force. He told us the gangs move freely around the region.

"They don't recognise borders. They commit crimes in El Salvador, flee El Salvador to come to the US and you have MS-ers who are committing crimes in the US and fleeing down to El Salvador to evade arrest."

Hard fist

But once in El Salvador, the challenge to authorities is immense.

Entire swathes of the capital are virtually under the control of MS-13 and its rival, Mara 18.

Local police patrol warily, tending when possible to avoid those parts of the city.

The region's homicide rates are among the highest in the world - 58 per 100,000 of population in El Salvador.

The past decade has seen politicians rise to power on the back of promises to declare war against the gangs.

The "Mano Dura" - or Hard Fist - policy introduced by Honduras at the start of the decade was closely followed by "Super Mano Dura" in El Salvador.

The legislation meant police could round up gang members at will, throwing young men in prison for any suspicious behaviour, including associating with likely gang members or sporting tattoos.

The result was thousands of gang members in prison.

But courts were not able to process such numbers and many lingered in prison without charge.

The prisons themselves have become strongholds of the gangs, many of them controlled by the Maras themselves, the authorities guard only from the outside.

The "Mano Dura" policies are now largely discredited.

On patrol in San Salvador, the police told us the laws had been counter-productive, driving the gangs underground and leading to more clever tactics from the likes of MS-13.

They pointed out men who could be Maras, but who now wear long t-shirts to cover their tattoos.

The graffiti that used to be ubiquitous, identifying each gang's territory, is no longer so obvious.

Mano Dura made the prisons into virtual headquarters for the gangs.

And the US deportation policy added to the problem, with the result that the gangs have become ever more organised and powerful.

Revolving door

Jose Miguel Cruz, of the University of Central America, who has studied the Maras for over a decade, says these approaches have led to a "revolving door" effect.

"MS-13 has spread across the US and is a major security problem in Central America. We haven't tried any more preventative measures."

He draws a comparison with Nicaragua. "They also are poor, they also have weak institutions."

If we can lock them away we will but if we can't, they should be deported Julie Myers, US assistant secretary of state for homeland security

But Nicaragua has so far managed to avoid any large-scale gang problem. Why? "The police concentrate on more preventative measures," says Mr Cruz.

Former gang member Edgar Ramirez backed this up.

When he arrived back from the US, deported after a three-year prison sentence, he said there were no opportunities, no way back into normal society.

"I had tattoos so everyone treated me like a criminal," he tells us.

"And if you speak English, they know you're a deportee."

For now, US policy remains focused on law-enforcement.

The US Assistant Secretary of State for Homeland Security, Julie Myers, says it must remain the priority.

"If we can lock them away we will, but if we can't, they should be deported," she told us.

"We have to think about stopping young people going into gangs; but I believe the American public is safer when we remove these individuals from the streets of our communities and deport them wherever possible."

In the 1980s, when Ronald Reagan was fighting a proxy war against the Soviet Union in Central America, he promised to rebuild a new, better, El Salvador.

But after spending so much on the war, there was little appetite in Washington for the reconstruction project.

Two decades later, the US is reaping the consequences. And in Central America, a region still struggling with poverty and crime, MS-13 has thrived.

Law enforcement alone does not seem to be enough to contain it.

The Maras: the Most Dangerous Gang in America for the Assignment programme was broadcast by the World Service. Click here for the podcast.